1. Field of the Invention
The present invention relates to a servo motor control system for controlling servo motors for shafts in machines such as various industrial machines, machine tools, and robots.
2. Description of the Related Art
In a servo motor control system, a numerical control device and servo amplifiers for driving and controlling servo motors are connected to each other with a serial bus, and the numerical control device exchanges data used to control the servo motors with the servo amplifiers through the serial bus. As a connection system between the numerical control device and the servo amplifiers with a serial bus, a daisy chain system achieved by an optical cable is known (for example, see Japanese Unexamined Patent Publication No. 10-13394).
When bit rates in serial communication between the numerical control device and the servo amplifiers or between the servo amplifiers are different from each other, communication between the numerical control device and the servo amplifiers or between the servo amplifiers cannot be established. A common bit rate must be used in communication between elements constituting the servo motor control system. When the servo motor control system is structured at the first, one data transfer system is employed at the same bit rate.
However, when some element (numerical control or servo amplifier) of the system breaks to exchange the broken element with a new element in use of the servo control system, bit rates may be changed to employ a different data transfer system. In particular, when a bit rate is high, an amount of data exchanged between the numerical control device and the servo amplifiers increases. For this reason, a new product tends to employ a transfer system in which a bit rate higher than a conventional bit rate is set. For this reason, when a new product is built as an element of an existing servo motor control system, bit rates are changed, the system cannot operate. This problem is frequently posed in a servo motor control system in a machine such as a machine tool having a long life.